Angelo Agostino

Characterisation of colourants on illuminated manuscripts by portable fibre optic UV-visible-NIR reflectance spectrophotometry

The use of ultraviolet and visible diffuse reflectance spectrophotometry as a preliminary technique in the investigation of illuminated manuscripts is discussed. Because ancient manuscripts are amongst the most fragile and precious artworks, characterisation of the materials used in their decoration should be performed using non-invasive analytical methods. Ultraviolet and visible reflectance spectrophotometry with optical fibres (FORS) allows non-invasive identification of several colourants used by ancient illuminators, causing no damage or mechanical stress to the artworks subjected to analysis. Identification is usually based on the comparison of analytical data with a spectral database built from painted areas on parchment, created by preparing paints according to ancient recipes as described in medieval technical treatises. Such database and the spectral features of the colourants analysed are discussed, along with the benefits of extending the spectral range of analysis into the shortwave infrared (to 2500 nm). FORS can be best appreciated as a rapid preliminary tool that offers an overview on the main colourants employed and guides the selection of painted areas of manuscripts on which more selective techniques, such as X-ray fluorescence or Raman spectroscopy, can be employed for a more complete and accurate identification.

Non-invasive investigation on a VI century purple codex from Brescia, Italy

Purple codices are among the most relevant and prestigious book productions of Late Antique and Medieval age. They usually contained texts from Holy Writings written with golden or silver inks on parchment dyed in a purple hue. According to the tradition, the colour of parchment was obtained by the well renowned Tyrian purple dye. From the material point of view, however, very little is known about the compounds actually used in the manufacture of these manuscripts. Presently, the information available is limited to the ancient art treatises, with very few diagnostic evidences supporting them and, moreover, none confirming the presence of Tyrian purple. It is more than apparent, then, the need to have at disposal larger and more complete information at the concern, in order to verify what came to us from the literary tradition only. In this study, preliminary results are presented from non-invasive investigation on a VI century purple codex, the so-called CodexBrixianus, held in the Biblioteca Civica Queriniana at Brescia (Italy). Analyses were carried out with XRF spectrometry, UV-visible diffuse reflectance spectrophotometry, molecular spectrofluorimetry and optical microscopy. The results suggest the hypothesis that Tyrian purple had been used as a minor component mixed with other less precious dyes such as folium or orchil.

Control of the oxygen doping in Bi-2212 whiskers by means of their synthesis process

Direct evidence of oxygen doping control in single phase Bi2Sr2CaCu2O8+δ (Bi-2212) whiskers is reported, along with the changes in their structural properties obtained by varying the growth temperature of the synthesis process in the range from 843 to 872 °C. The as-grown whiskers were investigated by means of x-ray powder diffraction (XRPD), electrical transport measurements, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The XRPD measurements showed that the value of the c-axis lattice parameter increases from 30.556 to 30.640 A when increasing the growth temperature, which indicates different oxygen doping levels spanning from the slightly overdoped to the nearly optimally doped regimes. Such results are also confirmed by the electrical characterizations, which revealed a typical relationship among resistivity (ρab), superconducting critical temperature (Tc), and c-axis value. The growth of CuO crystals has also been identified during this study, with a maximum yield in the range 860–864 °C, where also a slope change in the c-axis behavior has been found, implying a possible correlation between the two phenomena. Therefore, by changing the synthesis growth temperature, one can provide an effective way to tune the whisker electrical transport properties.

Growth, contacting and ageing of superconducting Bi-2212 whiskers

We report the growth of highly oriented microscopic whisker-like crystals in the Bi–Sr–Ca–Cu–O system by means of glassy precursors. The dependence of the growth on the stoichiometric composition and on the temperature and duration of the annealing process has been studied. Chemical impurities have been investigated from the point of view of the morphology, the elemental composition and the crystal structure, identifying the presence of CuAl2O4, Sr1.2Bi0.8O3 and Al. Electrical contacts have been fabricated by means of thermal evaporation and diffusion. Their sizes have been carefully measured, achieving contact resistivity in the range of 0.2–3.7 × 10−6 Ω cm2. A very slow degrading of the contacts and the crystals on a time scale of a few years has been detected. This is associated with a decrease in Tc, which is probably due to oxygen release from the material.

Structural Characterization of Multi-Quantum Wells in Electroabsorption-Modulated Lasers by using Synchrotron Radiation Micrometer-Beams

Advanced optoelectronic devices, the backbone of modern communication technology, require the monolithic integration of different functions at chip level. An example of devices fulfilling this requirement are multi-quantum well (MQW) electroabsorption-modulated lasers (EMLs) employed in long-distance, high-frequency optical fiber communications technology. Such devices are realized by using the selective area growth (SAG) technique. Optimization of the growth parameters is carried out by empirical approaches as direct structural characterization of the MQW is not possible with laboratory X-ray sources, owing to the micrometer-variation of composition and thickness inherent to the SAG technique. Micrometer-resolved X-ray (m-X-ray) beam available at third generation synchrotron radiation sources, such as the ID22 at the European Synchrotron Radiation Facility (ESRF), allowed us to directly measure the determinant structural parameters of MQW EML structures such as well and barrier widths and mismatches with a 2 mm spatial resolution. In more detail, optoelectronic devices, widely used in the generation and detection of optical signal for telecom and datacom applications, consist of different III-V semiconductors alloys deposited on suitable substrates. The deposition can be performed by different techniques that are based on the crystal rebuilding of a semiconductor used as substrate, such as metal

A diagnostic study on folium and orchil dyes with non-invasive and micro-destructive methods.

Folium and orchil are dyes of vegetal origin. Folium is obtained from Chrozophora tinctoria (L.) A. Juss., whereas orchil is obtained from Roccella and other genera of lichens. These dyes were used in the past to impart purple hue to paintings and textiles as substitutes for the more prised Tyrian purple dye, obtained from shellfish. Despite several citations in ancient technical treatises dating back at least to the Greek-Roman age, the identification of these dyes in artworks is rare. In the case of folium, an additional drawback is that its composition is presently unknown. In this work different non-invasive (FT-IR, FT-Raman, fibre optic reflectance spectrophotometry, spectrofluorimetry, X-ray fluorescence spectrometry) and micro-invasive (surface enhanced Raman spectroscopy, matrix assisted laser desorption ionisation-time of flight-mass spectrometry, inductively coupled plasma-mass spectrometry) techniques were used in order to increase the diagnostic information available on these dyes. Measurements were carried out on the dyes extracted from raw materials and on painted or dyed parchments. The possibility to distinguish between folium and orchil by chemical analysis is discussed.

Magnetic shielding efficiency of superconducting/ferromagnetic systems

We studied magnetic flux penetration in a hybrid MgB2/Fe structure consisting of two coaxial cups in a magnetic field applied parallel to their axis. This analysis was performed to investigate the potential of magnetic shielding of systems with a reduced length/radius aspect ratio exploiting the opposite magnetic properties of superconducting and ferromagnetic materials. We measured the field attenuation for applied magnetic fields up to 1.5?T, in different positions along the cup axis. At higher fields, the hybrid solution gives shielding factors up to more than three and four times higher than those of the MgB2 cup alone at T?=?20 and 30?K, respectively. This improvement changes as a function of the applied field and of the position along the cup axis and cannot be explained as a straightforward composition of the independent shielding contributions of the ferromagnetic and superconducting layers.

Study of epitaxial selective area growth In1−xGaxAs films by synchrotron μ-XRF mapping

We present an analytical method allowing to quantitatively extract, from a space resolved Synchrotron Radiation X-Ray Fluorescence (SR-XRF) map, the variation of the thickness and chemical composition of a In1−xGaxAs ternary semiconductor film, in which a gradient in the growth plane of both composition and thickness is obtained using the Selective Area Growth (SAG) method. This advanced growth technique allows the realization of monolithic integrated laser/modulator devices for long distance fiber optics communication at high frequency, which have recently come to the market as high performance products. In a SAG growth, the optimization of the growth parameters is usually done by an empirical approach since a spatially resolved compositional characterization is not possible with conventional laboratory techniques. Exploiting the μ-X-ray beam available at the ID22 beamline of the European Synchrotron Radiation Facility (ESRF), we performed a 2D micrometric resolved (1.7 × 5.3 μm2) XRF study of a In1−xGaxAs ternary semiconductor film. The purposed method is a theoretical influence coefficient algorithm based on the use of only few reference materials coupled with the fundamental parameter (FP) approach and it is optimized for intermediate thickness samples. Reported values agree quantitatively with independent High Resolution X-Ray Diffraction (HRXRD) analysis within 1%.

μ -EXAFS, μ -XRF, and μ -PL Characterization of a Multi- Quantum-Well Electroabsorption Modulated Laser Realized via Selective Area Growth

In the past few years, strong efforts have been devoted to improving the frequency of optical-fiber communications. In particular, the use of a special kind of integrated optoelectronic device called an electroabsorption modulated laser (EML) allows communication at 10 Gb s(-1) or higher over long propagation spans (up to 80 km). Such devices are realized using the selective area growth (SAG) technique and are based on a multiple quantum well (MQW) distributed-feedback laser (DFB) monolithically integrated with a MQW electroabsorption modulator (EAM). Since the variation in the chemical composition between these two structures takes place on the micrometer scale, in order to study the spatial variation of the relevant parameters of the MQW EML structures, the X-ray microbeam available at the ESRF ID22 beamline is used. The effectiveness of the SAG technique in modulating the chemical composition of the quaternary alloy is proven by a micrometer-resolved X-ray fluorescence (μ-XRF) map. Here, reported micrometer-resolved extended X-ray absorption fine structure (μ-EXAFS) spectra represent the state of the art of μ-EXAFS achievable at third-generation synchrotron radiation sources. The results are in qualitative agreement with X-ray diffraction (XRD) and micrometer-resolved photoluminescence (μ-PL) data, but a technical improvement is still crucial in order to make μ-EXAFS really quantitative on such complex heterostructures.

Doping change in the Bi-2212 superconductor directly induced by a hard X-ray nanobeam.

We describe the controlled use of a 17 keV X-ray synchrotron nanobeam to progressively change the oxygen doping level in Bi-2212 superconducting whisker-like single crystals. Our data combine structural and electrical information collected on the same crystals, showing a maximum change in the critical temperature Tc of 1.3 K and a maximum elongation of ∼1 Å in the c-axis length, compared to the as-grown conditions. Simulations of our experimental conditions by means of a finite element model exclude local heating induced by the X-ray nanobeam as a possible cause for the change in the doping level and suggest an important role of secondary electrons. These findings support the possible use of hard X-rays as a novel direct-writing, photoresist-free lithographic process for the fabrication of superconducting devices, with potential nanometric resolution and 3D capability.